Numerous approaches have been taken to automatic loading of firearms using a magazine affixed to the barrel or stock of the weapon and with cartridges stored in end-to-end relation for selective advancement into a receiver chamber. The use of a single chamber poses definite restrictions on the number of cartridges or shells that can be loaded from each magazine and this is especially true with respect to shotguns which utilize larger sized shells.
It has been proposed in the past to provide a magazine having circumferentially arranged chambers, each chamber containing shells in end-to-end relation and the chambers being rotatable into alignment with a receiver chamber for discharging the shells from each chamber into the receiver. For instance U.S. Pat. No. 4,905,395 to Wagner discloses housing sections with a plurality of shell holding chambers, the chambers being rotated by a spring member to position each loaded chamber into alignment with the receiver after which an indexing mechanism will cause the shells within each chamber to advance toward the receiver. In order to load the magazine, a turning knob in the housing must be manually engaged to wind the rotation spring so that once fully loaded the spring will have enough tension to automatically rotate each chamber in succession into alignment with the receiver.
In U.S. Pat. No. 1,420,471 to Carter a plurality of magazine tubes are successively advanced into alignment with a loading port, each tube in succession being manually rotated into alignment. Wilson U.S. Pat. No. 618,369 discloses a magazine with multiple chambers each loaded with a series of shells in tandem but which require manual rotation to bring each successive shell into alignment with a receiver.
An important consideration in an automatic loading device for firearms is the ability to maximize the number of shells which can be stored in the magazine without undue increase in size or weight of the firearm. In this regard it is important that the magazine be readily attachable to existing firearms and that the shells can be automatically advanced for successive loading into a receiver chamber in a positive, reliable manner without any special manipulation by the operator other than the usual pump action required in loading the shells into the firing chamber. In particular it is desirable that a magazine can be designed with circumferentially arranged chambers coextensive with one another, each storing a plurality of shells and each chamber is automatically advanced into alignment for loading of its shells into the receiver chamber after the preceding chamber has been emptied.